Yeah, another vote here. We did it a few years back and it was fantastic. Saw loads of Dolphins who put on a great show. I think you would be unlucky not to see any. The guide said the dolphins had gotten used to the sound of the Sea Screamer and nearly always came "out to play" in its wake as it is one of the fastest boats around.
TIP: When you park up at the marina, there is a building with a small shop, toilets and a cafe....if you go in here first, pick up some coupon books and you can get a couple of $$ off the Sea Screamer. It was about $16 when we did it in '99.
Not sure it would be suitable for very young kids (under 5s??) as it throws you around a bit. Life jackets are available though.
Allie